Treatment of material particles



July 21, 1942. B. HORSFIELD TREATMENT OF MATERIAL PARTICLES Filed May 26, 1959 Q a 35m d N .R film O Tm Q MA o H 1 M Patented July 21, 1942 Basil Horsileld, Pittsburgh, Pa, assimito Edwin- L. Wiegand, Pittsburgh, Pa.

Application May 26, 1939, Serial No. 275,961

19 Claims.

My invention relates to the treatment of material in the form of particles, to remove foreign material of slime nature, either co-mingled with the particles or adhering to the particles, and, more particularly to remove objectionable coatings from the individual particles, and the principal object of my invention is to provide a new and improved method of such treatment.

One material to which my method may be applied is zircon sand or ore. The particles of this desired that the particles be ground to greater fineness, but that the undesirable coatings be material often are found to have films or coatings of iron oxide or some other foreign material or combination of foreign materials. These coatings are usually in the form of a more or less complete shell surrounding the individual particle. These foreign materials are objection able, particularly if the zircon is to be used as electrical insulating material, for example. A

very small amount of such foreign material will make a very great' difierence in the resistivity of a mass of insulatingmaterial, particularly if the material is subjected to elevated temperatures. While zircon has been given as an example, it will be understood by those skilled in the art that my invention may be applied in connection with other similar insulating materials, or other materials.

In the single figure of the drawing accompanying this specification, and forming a partof this application, I have shown, for purposes of illustration, one embodiment of my invention in more or-less diagrammatic form.

The material to be treated in accordance with my invention may be first subjected to preliminary treatment such as rough screening, screeningto size, magnetic separation, soaking, washing, and so forth, as may be desired or considered necessary in connection with the particular material.

The material, preliminarily treated or'not, as

' the case may be, is introduced into a hopper I 0 through a conduit II, or in any other suitable way. The hopper ID has an outlet l2 suitably connected, as by a pipe 13, w th the feed end .of a rotary tumbling barrel or ill I, this mill being here shown, diagrammatically, as of the type commercially known as a Hardinge conical ball mill. It is desired that the material be treated in the mill ll in the presence of water, and, if the material fed into the hopper i0 is not already mixed with water, water may be fed into the hopper Iii by a conduit l5, or otherwise fed to the material. In practicing my method it ispreferred that'the mill l4 contain no balls or other like grinding bodies as it is not 55.

in filling the mill.

scufied therefrom. The desired scufiing action is produced by self-attrition, that is, by movement of the surface of a particle upon the surface of another particle. Such movement is caused by the rotation of the mill t4 and. resultant tumbling of the material. In the mill M, the material more or less settles from the liquid in the mill, thus increasing the rubbing or scufllng action as the mill rotates.

. It will be understood that the speed of the mill will control to some extent the nature of the scufling action. The speed should not be high enough to lift the material through an arc of but should turn the load on itself somewhat below this angle. For. a gentle attrition 10 R. P. M. is desirable but speeds up to 40 R. P. M. or more may be used depending somewhat upon the nature of the material being treated and the size of the min. In the case of treating zircon,

it is desired to remove any coating of foreign .material and not to abrade the crystal surface but scuif it clean. For this material, I have found in medium size conical mills of 4 feet diameter'or larger, that from 10 to 20 R. P. M. is a desirable operating speed. The. time of milling is also important. I have found that, in the treatment of zircon to be used for electrical purposes, a time of from 4 to 6 hours is desirable.

However, the time may be greatly extended, particularly if the mill is operated at a very low speed, or the time may be shortened to an hour or somewhat less, depending uponthe particular material to be treated. thespeed of the mill,

and the results desired. I have found. that even a small amount of self-attrition produced in the millproduces a material which gives results which are measurably better than. a material which has not been so. treated.

It will be understood that the material may be treated in the mill ll as-a batch for the desired period of time, or material may be continuously fed into the mill and continuously discharged therefrom, in which case the dwell in hours, of the material in the mill, is on the average equivalent to the charge carried by the mill continuously, divided by the hourly feed rate Preferably, a basic solution is fed to the material to be treated at a suitable-i and desired place, or places. A receptacle l6 containing such a solution is here shownas connected by a pipe ll through a valve II to the hopper l0, enabling a quantity of the basic solution to be added to the material in the hopper Ill, and hence to the material in the mill I4, and to the material in a separator, as will appear. The basic solution may be added continuously in accordance with continuous feed of material through the pipe l3 to the mill l4.

I have found that with an acid solution, that is, a solution where pH is less than 7, in the mill M, the scufiings, though mechanically separated from the particles by the action in the mill, tend to cling to the particles, probably due to an electrostatic efiect, thereby hindering a separation of the particles from the scuiiings. On the other hand, I have found that in a basic orneutral solution the scufilngs do not cling to the particles but are in suspension in the liquid. Desirably, the hydrogen ion concentration of the solution in the mill [4 is made such that pH is equal to 8 or more. Ammonium hydroxide may be used as the basic material, and this material has the further advantage of being a dispersing agent of high basicity, as well as being completely volatile without residue, but any other suitable material may be utilized.

The material treated in the mill I4 is discharged therefrom through a conduit l9 to the feed end of a washer or slime separator 20, such as, for example, of the Akins, Dorr, Hardinge or other suitable type. The separator 20-is here diagrammatically shown as comprising a tank 2|, the bottom 22 of which is inclined upwardly to a discharge outlet 23. The heavy, desired par-. ticles settle to the bottom of the tank 2| while the slime or scuffings and other undesirable particles tend to float on top of the liquid in the tank. The material that settles to the bottom of the tank-2| is constantly urged toward the outlet 23 in any suitable way, as by means (not shown) of rakes, screws, or the like. Movement of the desired material to the discharge outlet 7 23 is somewhat impeded by the action of a counter stream of water issuing from a Jet 24, and the counter-current thus provided carries the slime and scufiings and other rejects to an outlet 25. The outlet 25 maintains a constant liquid level in the tank 2|, the overflow liquid together with the rejects carried thereby being discharged through the outlet 25 into a receptacle-2B if desired. While the'particles discharged into the receptacle 26 have been termed rejects, it will be understood that under some conditions these particles may also have value, for purposes other started, the feed to the mill is increased and the discharge is increased, inasmuch as the level in the mill is quite constant. By reason of recirculation of washed material the amount of dirt in the mill is in lower ratio to the contents. Inasmuch as the previously washed material becomes admixed with the new material, it has ,zirconsand, which comprises zircon crystals lying for the most part between 60 and 150 mesh. Zircon which has been treated in accordance with my invention has exceptionally high resistance to the passage of current at elevated temperatures, and hence is particularly desirable for use as refractory electrical insulating material. Zircon is usually marketed as a concentrate from beach sands. Zircon concentrate is produced from beach sands which contain commercial quantities, by hydraulic and magnetic treatment for the removal of silica and other light silicates and for the removal of ilmenite with which it is associated. The zircon sand may also have been treated by flotation, for removal of rutile with which it is associated, and in that case the par.-

' ticles of zircon are covered with a film of flotation re-agents, such as oils, greases, acids, etc. which are not only difiicult .to remove but-tend to collect other matter as a coating and fix it to the zircon grain. Furthermore, it is believed that zircon crystals subjected to the action of sea water for long periods become covered with a coating or film of one kind or another, either mechanically or of a chemically precipitated nature, or both. It is possible that, from the sea water, a certain absorption of the alkali or metal halides, or both, takes place on the surface of the zircon. In the case ,of some kinds/of films, such as iron oxide films, the coating is visible,-but often the coatingis not subject to visual estimation either quantitatively or qualitatively. I

than the particles discharged from the outlet 23.',

It will be evident that the dispersing agent hereinbefore referred to serves the twofold purpose of enabling easy and efflcient separation of the desired particles from'the foreign matter in the separator 20, and of promoting self-attrition of the particles in the mill l4.

From the outlet 23 of the separator 20 the material may pass by way of a conduit 21 to any other apparatus which may be desired for further treatment of the material, and the material is eventually dried.

If desired, approximately one-half, or any selected suitable fraction of the material discharged fromthe outlet 23 of the separator 20 may be returned to the mill I4, and this is diagrammatically indicated by a conduit 28, here shown as receiving material from the outlet 23 and carrying it, as indicated by the arrows, to the hopper [0. Introduction into the mill ll of scuffed, washed particles along with unscufied particles promotes and scufllng in the mill of the unscufied particles, When recirculation of material is have found through extended research that while some of these coatings are acid soluble or soluble in alkalis, or, in the case of flotation products, are soluble in commercial solvents, the electrical resistivity ofa mass of particles so cleaned is often reduced instead of increased owing to some further phenomena brought about by the chem-.

out under conditions which free the particles from the matter removed, as in the presence of a dispersing agent, as hereinbefore referred to, the zircon so treated shows electrical resistivity, measured through a compacted mass of grain at a temperature of 1600 F., at least 7 times greater than zircon cleaned by simple washing. In addition, whereas different lots of similar zircon of untreated grain varied in electrical resistance value over wide ranges, the grain produced from treated zircon maintained a high average resistthe presence of water, subjecting the material ance. In the treatment of zircon for electrical purposes, in accordance with my invention, I prefer to use ammonia as a dispersing agent, as it is a carbon-free and a metal-free base, but I do not limit myself to this dispersing agent, as other dispersing agents of similar qualitymay be substituted. In the case of producing grain zircon for mechanical uses which demand the properties of zircon alone without interference by possible fluxing properties of coating materials, dispersing agents may be chosen on a basis of desired results as to mechanical cleanliness.

From the foregoing it will be apparent to those skilled in the art that the illustrated embodiment of my invention provides a new and improved method of treating materials, and accordingly, accomplishes the principal object of my invention. .On the other hand, it also will be obvious to those skilled in the art that the illustrated embodiment of my invention may be variously changed and modified, or features thereof, singly or collectively, embodied in other combinations than those illustrated, without departin from the spirit of my invention, or sacrificing all of the advantages thereof, and that accordingly, the disclosure herein is illustrative only, and my invention is not limited thereto.

I claim:

1. The method of treating material particles comprising particles of refractory crystalline mineral material intended for use as electrical insulating material, which comprises, subjecting the particles to self attrition in the presence of a liquid containing a dispensing agent which is carbon-free and metal-free.

2. The method of-cleaning discrete particles of hard crystalline mineral material, which comprises, charging a rotary tumbling mill so that the charge therein comprises only a liquid and the discrete particles, said liquid including a dispersing agent, causing the particles to be so tumbled in said mill that said'particles constitute a substantially unitary tumbling mass, separating particles from cleanings, and returning a portion of said separated particles'to mingle with the charge in said mill. 7

3. The method of cleaning discrete particles of crystalline mineral material comprising particles intended for use as electrical insulating material, which comprises, charging a rotary tumbling mill so that the charge therein comprises only a liquid and the discrete particles, causing the particles to be so tumbled in said mill that said particles constitute a substantially unitary tumbling mass, subjecting the material to a dispersing agent which is'carbon-free and metal-free, and separating the particles from the cleanings.

4. The method of cleaning discrete particles of hard crystalline mineral material intended for use as electrical insulating material, which comprises, charging a rotary tumbling mill so that the charge therein comprises only a liquid and the discrete particles, said liquid including a dispersing agent which is carbon-free and metalfree, causing-the particles to be so tumbled in said mill that said particles constitute a substantially unitary tumbling mass, separating particles from cleanings, and returning a portion of said separated particles to mingle with the charge in said mill.

5. The method of treating material particles,

. which comprises, in a prior stage subjecting a mass consisting of discrete particles of hard crystalline mineral material to self attrition only, in

to a dispersing agent, separating particles from cleanings, and returning a portion of said separated particles to mingle with particles being treated in said prior stage. I

6. The method of treating material particles, which comprises, in a prior stage subjecting a mass consisting of discrete particles of hard crys-" talline mineral material to self attrition only, in the presence of water, subjecting the material to a dispersing agent while it is being subjected to self attrition, separating particles from cleanings, and returning a portion of said separated particles to mingle with particles being treated in said prior stage.

'7. The method of removing foreign coatings from zircon grains to produce clean zircon grains for use in electrical refractory, which comprises, subjecting raw material consisting of discrete material particles comprising natural grain zircon to mutual rubbing action" in the presence of water and in the absence of grinding bodies, treating the material with a dispersing'agent which is carbon-free and metal-free, and separating the particles from the cleanings. o

8. The method of removing foreign coatings from zircon grains to produce clean zircon grains for use in electrical refractory, which comprises, subjecting raw material consisting of discrete material particles comprising natural grain zircon to mutual rubbing action in the presence of water and in the absence of grinding bodies, treating the material with a dispersing agent which is carbon-free and metal-free, separating particles from cleanings, and returning a portion of said separated particles'to mingle with particles being subjected to mutual rubbing action.

9. The method of removing foreign coatings from zircon grains to produce clean zircon grains for'use in electrical refractory, which comprises, subjecting a mass consisting of discrete m'aterial particles comprising natural grain zircon to self attrition only, in the presence of water in a rotary tumbling mill, subjecting the material to a dispersing agent which is carbon-free and metalfree, and separating the particles from the cleanings.

10. The method of removing foreign coatings from zircon grains to produce clean zircon grains for use in electrical refractory, which comprises, subjecting a mass consisting of discrete material particles comprising natural grain zircon to self attrition only, in the presence of water in a rotary tumbling mill, said water containing a dispersing agent which is carbon-free and metalfree, separating particles from cleanings, and returning a portion of said separated particles to mingle with the particles in said mill.

11. The method of removing foreign coatings from discreteparticles of hard crystalline mineral material to produce clean particles, which comprises, subjecting raw material consisting of such discrete particles to mutual rubbing action grinding bodies, said water containing a dispersing agent, hydraulically separating particles from cleanings, and returning wet separated particles to mingle with particles being subjected to mutual rubbing action.

- 13. The method of removing foreign coatings from zircon grains to produce clean zircon grains, which comprises, subjecting raw material consisting of discrete particles comprising natural grain zircon to mutual rubbing action in the presence of water and in the absence oi: grinding bodies, treating the material with a dispersing agent, hydraulically separating particles from cleanings, and returning wet separated particles to mingle with particles being subjected to mutual rubbing action.

14. The method of removing foreign coatings stitute a substantially unitary tumbling mass,

from zircon grains to produce clean zircon grains I for use in electrical refractory, which comprises, subjecting raw material, consisting of discrete material particles comprising natural grain zircon to mutual rubbing action in the presence of water and in the absence of grinding bodies, treating the material with a dispersing agent which is carbon-free and metal-free, hydraulically separating particles from cleanings, and returning wet separated particles to mingle with particles being subjected to mutual rubbing action.

15. The method of removing foreign coatings of crystalline mineral materialcomprising particles intended for use as electrical insulating material, which comprises, charging a rotary tumbling mill so that the charge therein comprises only aliquid and the discrete particles, said liquid comprising a dispersing agent which is carbonfree and metal-free, causing the particles to be so tumbled in. said mill that said particles conand separating the particles from the cleanings. 17. The method of removing foreign coatings from zircon grains to produce clean zircon grains for use in electrical refractory, which comprises,

subjecting a mass consisting of discrete material particles comprising natural grain zircon to self attrition only, in the presence of water in a rotary tumbling mill, said water containing a dispersing agent which is carbon-free and metal-free, and separating the particles from the cleanings.-

18. The method of removing foreign coatings from zircon grains to produce clean zircon grains,

which comprises, subjecting raw material confrom zircon grains to produce clean zircon grains for use in electrical refractory, which-comprises, subjecting a mass consisting of discretematerial particles comprising natural grain zircon to self attrition only, in the presence of water in a rotary tumbling mill, said water containing a dispersing agent which is carbon-free and metalfree, separating particles from cleanings, and returning separated particles to mingle with the particles in said mill.

16. The method of cleaning discrete particles sisting of discrete particles comprising natural grain zircon to mutual rubbing action in the presence of water and in the absence of grinding bodies, said water containing a dispersing agent, hydraulicallyseparating particles from cleanings, and returning wet separated particles to mingle with particles being subjected to mutual rubbing action.

19. The method of removing foreign coatings j from zircon grains-to produce clean-zircon grains, whi'chcomprises, in a prior stage subjecting a mass consisting of discrete particles comprising natural grain zircon to self attrition only, in the presence of water, subjecting the material to a dispersing agent, separating particles from cleanings, and returning separated particles to mingle with particles being treated in said prior stage.

BASIL HORSFIELD. 

